1. Field of the Invention
The present invention relates to an image forming apparatus, such as a copying machine, a facsimile apparatus, or a printer.
2. Description of the Related Art
Conventionally, an apparatus having a photosensitive member or the like includes a driving system having a driving motor, and resonance is caused by the oscillation as a result of the driving of this driving system. When the oscillation due to this resonance is transmitted to the exposure unit to cause the mirror to oscillate, the image will be blurred.
The primary resonance frequency of the mirror is higher than the frequency of the oscillation generated in the driving system, so that the mirror is free from resonance. However, a member extended between first and second frames is very subject to the resonance as a result of the driving of the driving system. When the member supporting the exposure unit resonates, the mirror is influenced by this resonance and oscillates.
The frequency of the driving system varies from one apparatus to another and depends on the driving condition, so that it is difficult to prevent the resonance from being transmitted to the exposure unit.
FIG. 5 shows a conventional apparatus. Numeral 304 indicates a flat exposure-unit supporting member. In this kind of apparatus, to cope with the above problem, a rubber member or the like is provided between the exposure unit 303 and the supporting member 304, or a diaphragm-shaped bearing surface for reinforcement is provided in the exposure unit mounting portion, thereby reducing the influence of the resonance of the supporting member.
If it is still impossible to reduce the influence of the resonance of the supporting member, the oscillation is suppressed by, for example, attaching a damping member to the exposure unit.
However, placing a damping member or the like between the exposure unit and the supporting member results in an unstable positioning of the exposure unit, a deterioration in the material of the damping member due to the use of long duration, etc., and the cost of solving these problems is rather high.
It is an object of the present invention to provide an image forming apparatus capable of reliably preventing the supporting member from being caused to resonate by the driving system by making the primary resonance frequency of the supporting member extending between a first frame and a second frame and supporting the exposure unit higher than that of the mirror in the exposure unit.
Another object of the present invention is to provide an image forming apparatus comprising:
a photosensitive member;
charging means for charging the photosensitive member;
an exposure unit for exposing the photosensitive member charged by the charging means to image information light to form an electrostatic latent image;
developing means for developing the electrostatic latent image on the photosensitive member;
transfer means for transferring the developed image on the photosensitive member to a transferring material;
a first frame and a second frame; and
a supporting member extending between the first and second frames and supporting the exposure unit,
wherein the supporting member has a primary resonance frequency higher than that of a mirror in the exposure unit.
Further objects of the present invention will become apparent from the following description.